Certain mechanical properties of wood, such as hardness, bending strength, compression properties and the like, may be improved by impregnating the wood with monomers or polymers. Whether the wood is impregnated with monomers, polymers, or a combination of both, the resulting wood is usually referred to as a wood-composite.
A well known process for producing a wood-composite involves immersing the wood to be treated in a fluid such as water, having dissolved therein a monomer or polymer, and subjecting the fluid to positive pressure to drive the monomer or polymer into the wood. This process is time consuming; large articles of wood require higher pressures and longer periods of time to complete the impregnating process vis a vis small articles of wood.
Variations of the known process include the use of negative pressure as well, or combinations of positive and negative pressures. Since impregnation by flow of monomer or polymer through the axial direction is the dominant mechanism, a major drawback of these known wood impregnation processes is that they are slow and result in non-uniform impregnation due to impenetrable pores. It is also known to impregnate wood with, say, methyl methacrylate (MMA) and to polymerize the MMA within the wood. One method for polymerizing polymerizable material in wood uses high energy radiation, for example, electron beam or gamma rays. This method requires a relatively high dosage of absorbed radiation which is costly. The prior art has also shown that lumber and wood veneers can be impregnated with plastic materials to improve and protect the surface of the wood. Furthermore, wood particles can be coated with plastic and compressed into various shapes.
This prior art knowledge is not limited to combinations of wood and polymer. For example, polymer impregnated paper, known as papreg and its laminates have been used in a wide range of applications. Similarly, impreg, a polymer impregnated laminated wood has been used for handles of utensils. If compressed, this impregnated laminate is referred to as compreg. There is also flapreg which is a polymer impregnated flakeboard and staypak, a polymer impregnated compressed, heat stabilized laminated veneer, which have found commercial uses.
Each of the prior art polymer impregnated wood and biomasses have been cumbersome, relatively expensive, and time consuming to produce.
Examples of prior art treatments for wood and other porous materials are shown in the following patents and publications:
______________________________________ 2,064,965 3,726,709 4,376,693 EP 1540 2,740,728 3,790,401 4,388,171 JA 135004 3,029,159 3,968,276 4,500,568 EP 45828 3,160,515 4,008,342 4,554,185 JA 1102206 3,183,114 4,308,200 4,576,838 JA 101311 3,200,003 4,167,597 4,596,724 3,579,369 4,313,976 Agnew 17,701 ('78) Chem. Wk. 14 Oct. '81 ______________________________________